Columbium alloy



United States Patent 3,138,206 COLUMBIUM ALLOY Arthur B. Michael, Lake Forest, Ill., assignor to Fansteei This application is a continuation-in-part of application Serial No. 824,783, filed July 3, 1959, and now abandoned, which in turn is a continuation-in-part of application Serial No. 754,938, filed August 14, 1958, now abandoned.

The present invention relates to metal alloys and particularly to .alloys and intermetallic compositions of columbium and tantalum.

There is described in Patent No. 2,957,764, issued October 25, 1960, alloys of columbium and tantalum which have high temperature oxidation resistance characteristics vastly superior to the high temperature oxidation resistance characteristics of either columbium or tantalum. A preferred embodiment of those alloys has an oxidation rate as low as about of the oxidation rate of substantially pure columbium. It has been found, however, that the high temperaure strength of the aforementioned alloys should be increased in order to provide such articles as turbine blades and buckets, rocket nozzles and other devices to be utilized in high temperature environments, with the physical characteristics that are desired for such devices.

Alloys embodying the present invention have high temperature strength characteristics substantially in excess of the high temperature strength characteristics ofthe columbium-tantalum binary alloys.

In accordance with the present invention, the physical characteristics, particularly at elevated temperatures, of columbium-tantalum base alloys are substantially improved when zirconium and/or titanium are added to the alloy. The addition includes zirconium in the range of from about 0.3% to about 5% by weight, or titanium in the range of from about 0.2% to about 2% by weight. When zirconium and titanium are used together, the total content thereof in the alloy should not be greater than about 5%, the minimum limit being about 0.3%.

Preferably, a zirconium when used alone is in the range of from about 0.5% to about 1.5% and the titanium when used alone is in the range of from about 0.5% to about 1.5%. The preferred range for the total zirconium and titanium, when the two are used together in the alloy, is in the range of from about 0.5 to about 1.5

The base metal for alloys embodying this invention is columbium with tantalum, the tantalum being in the range of from about 25% to about 40% by weight, but preferably in the range of from about 30% to about 35% by weight. The columbium, with small amounts of oxygen and carbon, which appear to play a role in the strengthening of the alloy in the presence of zicronium and/or titanium, with minor impurity constituents, constitutes the balance of the alloy. The oxygen content is preferably in the range from about .001% to about 0.1% and the carbon content is preferably in the range of from about .001% to about 0.1%.

In addition to the improved elevated temperature strength and oxidation resistance characteristics, the alloy has an excellent combination of fabricability, low temperature ductility and weldability. Further, the alloy has a substantially improved stress to rupture characteristic which increases, unexpectedly, with increases in zirconium within the described limits. For example, an alloy within the scope of this invention and having zirconium therein in an amount of about 0.67% by weight and about 35 ice tantalum by weight, had a stress to rupture characteristic of 30,000 pounds per square inch at 2,000 P. for a time greater'than five hours, and an ultimate tensile strength of 5,000 pounds per square inch at 2900 F.

When titanium is substituted for zirconium, the maximum effect of the titanium occurs when it is present in an amount of about 0.44% by weight. An alloy with such a content of titanium demonstrated properties similar to those set forth above for the alloy with about 0.67% zirconium and about 35 tantalum.

There is set forth below examples of alloys embodying this invention, results of tests of the alloys of those examples and exemplary procedures for making and testing the alloys. The examples are intended to be illustrative only and are'not intended to place any limits or re- 1 Example I An alloy or intermetallic composition of 63.43%

columbium, 35.77% tantalum, 0.67% zirconium, about 0.009% carbon, about 0.048% oxygen, and a minor quantity of impurities constituting the balance of the alloy was prepared by are melting an electrode of pressed and sintered powders of columbium, tantalum and zirconium having the specified proportions of constituents therein. In general, in this and the following examples, the tantalum material used had a purity of about 99.5 percent; the columbium used had a purity of about 99.2 percent; the zirconium used had a purity of about 99.8 percent; and the titanium used had a purity of about 99.8 percent.

The electrode was prepared by pressing a blend of powders of the materials at a pressure of about 50 tons per square inch to form a compact which was then sintered at a temperature of about 2000 C. and degassed for about two hours in a vacuum of about 1 or 2 microns. Preferred sintering temperatures were in the range of from about 1600 C. to about 2000 C. and preferred pressing pressures were in the range of from about 20 to about 50 tons per square inch. Other operable sintering conditions may be employed.

The are melting procedure was carried out by melting the composite electrode with an arc from a non-consumable electrode in an atmosphere of about 20 percent argon and about percent helium. The protective atmosphere, which should be an inert atmosphere, may be argon or helium or any other inert atmosphere that will not combine with the constituents of the alloy at elevated temperatures. If desired, the arc melting procedure may 'be efifected in a vacuum.

for tensile strength in a stress to rupture test showed a stress for rupture of about 30,000 pounds per square inch in a test conducted for more than five hours at 2000 F. The ultimate tensile strength of the alloy was 3 determined to be about 5,000 pounds per square inch at the extremely high temperature of about 2900 F.

In determining the oxidation rate, i.e., penetration, the dimensions of the test article were measured prior to subjecting the same to the oxidation test conditions. The oxidation scale which formed on the surface of the article during testing was removed, as by grit blasting or grinding, following which the thickness of the article was again measured. The change in dimensions provided the means of measuring the amount of metal lost by oxidation during the test period. The difference between the thickness of the original article and the thickness of the article following exposure thereof to the oxidation test conditions is referred to herein as penetration.

In determining the stress to rupture factor, a specimen of the alloy is subjected to tensile stress and heated to a temperature of about 2000 F., which temperature is maintained for a period suflicient for the specimen to rupture in tension.

A preferred test is conducted for a period of 100 hours at a tension such that the specimen will rupture. Usually several specimens are tested at varying tensile stresses for periods sufficient for the specimens to break. The breaking points and times of these specimens are then plotted and the 100 hour, 2000 F. stress for rupture factors are then determined from the plotted graph. This determined figure or factor is the factor which is used herein as the stress for rupture. Workability and fabrication characteristics were determined for the alloy. Samples were taken from the pieces worked for testing the ultimate tensile strength versus temperature and secondary creep rate.

For this purpose the arc melted ingot was coated with a protective frit and forged at a temperature in excess of about 2400 F. The forged pieces constituted rolling billets with dimensions of about 1 /2 thick by 6" wide.

Initial breakdown rolling which followed the forging was done warm with intermediate anneals. Finishing rolling to a thickness of about 0.087 was done at room temperature. High quality sheet was obtained from the alloy. High workability was indicated by the fact that after breakdown rolling cold reduction up to 94% was possible without intermediate anneals. The secondary creep rate was about 2.89 'l0 inches/inch/hour at 30,000 p.s.i. and 2000 F.

Example 11 An alloy or intermetallic composition of about 66.5% columbiurn, 32.8% tantalum, and 0.7% zirconium was prepared by the procedure set forth in Example I. That is, this alloy was prepared by pressing and sintering a lended mixture of metal powders in the proportions specified and are melting the sintered electrode in the manner set forth in Example I.

The resulting arc melted alloy, when tested, demonstrated about the same characteristics as those set forth for the alloy of Example I.

Example 111 An alloy or intermetallic composition of about 74.0% columbium, 25.6% tantalum and 0.4% Zirconium was prepared by the procedure set forth in Example I. The

alloy was prepared by pressing and sintering a blended mixture of metal powders in the proportions specified and are melting the sintered electrode in the manner set forth in Example I.

The resulting arc melted alloy, when tested for oxidation resistance in flowing air by subjecting the alloy to (1 Example IV An alloy or intermetallic composition of about 59.6% columbium, 39.4% tantalum and 1.0% Zirconium was prepared by the procedure set forth in Example I. The alloy was prepared by pressing and sintering a blended mixture of metal powders in the proportions specified and are melting the sintered electrode in the manner set forth in Example I.

The resulting arc melted alloy, when tested for oxidation resistance in flowing air by subjecting the alloy to a temperature of 2000 F. in flowing air for a period of sixteen hours, underwent an oxidation penetration of 0.010 cm. The hour stress for rupture at 2000 F. was 19,000 pounds per square inch.

These results compare very favorably with an oxidation penetration of 0.105 cm. and a 100 hour stress for rupture at 2000 F. of 13,000 pounds per square inch for substantially pure columbium subjected to the same test conditions.

Example V An alloy or intermetallic composition of about 62.2% columbium, 32.8% tantalum and 4.95% zirconium was prepared by the procedure set forth in Example I. The alloy was prepared by pressing and sintering a blended mixture of metal powders in the proportions specified and are melting the sintered article in the manner set forth in Example I.

The resulting arc melted alloy, when tested for oxidation resistance in flowing air by subjecting the alloy to a temperature of 2000 F. in flowing air for a period of sixteen hours, underwent an oxidation penetration of .014 cm. The 100 hour stress for rupture at 2000 F. was 18,000 pounds per square inch.

These results compare very favorably with an oxidation penetration of 0.105 cm. and a 100 hour stress for rupture at 2000 F. of 13,000 pounds per square inch for substantially pure columbium subjected to the same test conditions.

Example VI An alloy or intermetallic composition of about 67% columbium, 32.8% tantalum, and 0.2% titanium was prepared by the procedure set forth in Example I. The alloy was prepared by pressing and sintering a blended mixture of metal powders in the proportions specified and are melting the sintered article in the manner set forth in Example I.

The resulting arc melted alloy, when tested for oxidation resistance in flowing air by subjecting the alloy to a temperature of 2000 F. in flowing air for a period of sixteen hours, underwent an oxidation penetration of .010 cm. The 100 hour stress for rupture at 2000 F. was 18,000 pounds per square inch.

These results compare very favorably with an oxidation penetration of 0.105 cm. and a 100 hour stress for rupture at 2000 F. of 13,000 pounds per square inch for substantially pure columbium subjected to the same test conditions.

Example VII An alloy or intermetallic composition of about 66.7% columbium, 32.8% tantalum, and 0.5% titanium was prepared by the procedure set forth in Example I. The alloy was prepared by pressing and sintering a blended mixture of metal powders in the proportions specified and arc melting the sintered article in the manner set forth in Example I.

The resulting arc melted alloy, when tested for oxidation resistance in flowing air by subjecting the alloy to a temperature of 2000 F. in flowing air for a period of sixteen hours, underwent an oxidation penetration of .012 cm. The 100 hour stress for rupture at 2000 F. was 19,000 pounds per square inch. 7

These results compare very favorably with an oxidation penetration of 0.105 cm. and a 100 hour stress for rupture at 2000 F. of 13,000 pounds per square inch for substantially pure columbium subjected to the same test conditions.

Example VIII An alloy or inter-metallic composition of about 65.5% columbium, 33.1% tantalum, and 1.4% titanium was prepared by the procedure set forth in Example I. The alloy was prepared by pressing and sintering a blended mixture of metal powders in the proportions specified and are melting the sintered article in the manner set forth in Example I.

The resulting arc melted alloy, when tested for oxidation resistance in flowing air by subjecting the alloy to a temperature of 2000 F. in flowing air for a period of sixteen hours, underwent an oxidation penetration of .014 cm. The 100 hour stress for rupture at 2000 F. was 18,000 pounds per square inch.

These results compare very favorably with an oxidation penetration of 0.105 cm. and a 100 hour stress for rupture at 2000 F. of 13,000 pounds per square inch for substantially pure columbium subjected to the same test conditions.

Example IX An alloy or intermetallic composition of about 66.3% columbium, 32.85% tantalum, 0.5% zirconium and 0.35% titanium was prepared by the procedure set forth in Example I. That is, this alloy was prepared by pressing and sintering a blended mixture of metal powders in the proportions specified and are melting the sintered article in the manner set forth in Example I.

The resulting arc melted alloy, when tested for oxidation resistance in flowing air by subjecting the alloy to a temperature of 2000 F. in flowing air for a period of sixteen hours, underwent an oxidation penetration of .012 cm. The 100 hour stress for rupture at 2000 F. was 19,500 pounds per square inch.

These results compare very fiavorably with an oxidation penetration of 0.105 cm. and a 100 hour stress for rupture at 2000 F. of 13,000 pounds per square inch for substantially pure columbium subjected to the same test conditions.

It should be understood that numerous modifications and variations may be effected without departing from the true spirit and scope of the novel concepts and principles of this invention. The foregoing detailed description of the invention and embodiments thereof is given for clearness and for understanding of the invention, and no unnecessary limitations should be understood or implied therefrom, since some modifications will be obvious to those skilled in the art.

I claim:

1. A columbium-tantalum base alloy having improved high temperature strength and high temperature oxidation resistance at elevated temperatures consisting essentially of from about 2.5% to about 40% by weight tantalum, and from about 0.3% to about 5% by weight zirconium, the balance being substantially all columbium.

2. A columbium-tantalum base alloy having improved high temperature strength and high temperature oxidation resistance at elevated temperatures consisting essentially of from about 30% to about 35% by weight tantalum, and from about 0.5% to about 1.5% by weight zirconium, the balance being substantially all columbium.

3. A columbium-tantalum base alloy having improved high temperature strength and high temperature oxidation resistance at elevated temperatures consisting essentially of from about 30% to about 35% weight tantalum, and from about 0.5% to about 1.5% by weight zirconium, the balance being substantially all columbium, with carbon in the range of from about 0.001% to about 0.1% and oxygen in the range from about 0.001% to about 0.1%.

4. A columbium-tantalum base alloy having improved high temperature strength and high temperature oxidation resistance, consisting essentially of about 63.4% columbium, about 35.8% tantalum, about 0.7% zirconium and up to about 0.1% of impurities.

5. A columbium-tantalum base alloy having improved high temperature strength and high temperature oxidation resistance at elevated temperatures, consisting essentially of about 66.5% columbium, about 32.8% tantalum and about 0.7 zirconium.

6. A columbium-tantalum base alloy having improved high temperature strength and high temperature oxidation resistance consisting essentially of about 35.8% tantalum, about 0.7% zirconium, about 0.01% carbon, about 0.048% oxygen, and the remainder being substantially all columbium.

References Cited by the Examiner UNITED STATES PATENTS 2,822,268 2/58 Hix 174 2,957,764 9/60 Michael 75-l74 3,012,883 12/61 Allen 75---174 3,027,255 3/62 Begley et al. 75-l74 3,038,798 6/ 62 Berger et al. 75-174 BENJAMIN HENKIN, Primary Examiner. RAY K. WINDHAM, WINSTON A. DOUGLAS,

Examiners. 

1. A COLUMBIUM-TANTALUM BASE ALLOY HAVING IMPROVED HIGH TEMPERATURE STRENGTH AND HIGH TEMPERATURE OXIDATION REISISTANCE AT ELEVATED TEMPERATURE CONSISTING ESSENTIALLY OF FROM ABOUT 25% TO ABOUT 40% BY WEIGHT TANTALUM, AND FROM ABOUT 0.3% TO ABOUT 5% BY WEIGHT ZIRCONIUM, THE BALANCE BEING SUBSTANTIALLY ALL COLUMBIUM. 